1. Field of the Invention
The present invention relates to a method of producing an electrically responsive composite material configurable for application in a transducer. The present invention also relates to an electrically responsive composite material configurable for application in a transducer. The present application also relates to a method of fabricating a transducer and to a transducer having a substrate for supporting a flowable polymer liquid.
2. Description of the Related Art
An electrically responsive composite material configurable for application in a transducer is described in U.S. Pat. No. 6,291,568. The composite material includes electrically conductive particles dispersed within and encapsulated by a non-conductive polymer. The nature and concentration of the particles is such that the electrical resistivity of the material is variable in response to distortion forces being applied thereto. However, the polymer material is not in a liquid form which in turn restricts the total number of applications for which the material may be deployed. Furthermore, the disclosed material relies on the presence of void-bearing particles with protrusions such that electric fields are concentrated and conduction is permitted by field-assisted quantum tunnelling. However, it has been found, that materials of this type introduce undesirable levels of electrical noise when deployed in transducer applications.
An electrically responsive composite material configurable for application in a transducer is described in WO 2008/135,787, the whole contents of which are included herein by way of reference. The disclosed material has a substantially non-conductive polymer with first electrically conductive particles that have void-bearing structures in combination with second electrically conductive particles that are acicular in shape. The polymer material described in WO 2008/135,787 allows transducers to be developed that exhibit far superior noise characteristics due to the presence of the acicular particles. However, the presence of the void-bearing particles creates difficulties in terms of developing a flowable polymer liquid for application in a device, whereafter a transition is facilitated to convert the flowable polymer liquid into a resilient solid polymer.
An alternative proposal is identified in WO 2008/135,787 in which a non-conducting polymer is mixed with acicular conductive particles, with no void-bearing particles being present. The proposal of WO 2008/135,787 also identifies the possibility of manufacturing the composite material using a non-conductive solvent or water based polymer such that the material is usable as a flowable polymer liquid thereby facilitating its application in transducer devices. However, further problems have been identified with composite materials of this type when used in transducer applications.
Known devices do allow a resilient material to be formed (possibly by evaporation of a solvent) that exhibit a property to the effect that electrical resistance may vary when a force is applied. However, materials of this type show an inadequate response prior to the material becoming sensitive to the application of pressure. Thus, the inventors have found that the provision of spiky void-bearing particles present in the material described in U.S. Pat. No. 6,291,568 provides a first touch sensitivity. However, the presence of these particles has the disadvantage of introducing electrical noise and they are difficult to deploy in situations where a flowable polymer liquid is required for construction purposes.